为什么不自动调用超类__init__方法？ [英] Why aren't superclass __init__ methods automatically invoked?

问题描述

为什么Python设计者决定子类' __ init __（）方法不会自动调用 __ init __（）他们的超类方法，如在其他一些语言中？ Pythonic和推荐的成语是否真的如下？

Why did the Python designers decide that subclasses' __init__() methods don't automatically call the __init__() methods of their superclasses, as in some other languages? Is the Pythonic and recommended idiom really like the following?

class Superclass(object):
    def __init__(self):
        print 'Do something'

class Subclass(Superclass):
    def __init__(self):
        super(Subclass, self).__init__()
        print 'Do something else'

推荐答案

关键区别在Python的 __ init __ 和其他语言构造函数之间是 __ init __ 是不是一个构造函数：它是一个初始化程序（实际的构造函数（如果有的话，但是，见后面;-)是 __ new __ 和完全不同的工作方式）。虽然构建所有超类（并且毫无疑问，在继续向下构建之前这样做）显然是说你构建子类的实例，这显然是不是初始化的情况，因为有很多用例需要跳过，更改，控制超级类的初始化，如果有的话，在子类初始化的中间，

The crucial distinction between Python's __init__ and those other languages constructors is that __init__ is not a constructor: it's an initializer (the actual constructor (if any, but, see later;-) is __new__ and works completely differently again). While constructing all superclasses (and, no doubt, doing so "before" you continue constructing downwards) is obviously part of saying you're constructing a subclass's instance, that is clearly not the case for initializing, since there are many use cases in which superclasses' initialization needs to be skipped, altered, controlled -- happening, if at all, "in the middle" of the subclass initialization, and so forth.

基本上，初始化程序的超类委派在Python中不是自动的，原因完全相同，这种委托对于任何<而言也不是自动的/ strong>其他方法 - 并注意那些其他语言不会为任何其他方法执行自动超类委派... 只是用于构造函数（如果适用，析构函数） ，正如我所提到的那样，不 Python的 __ init __ 是什么。 （ __ new __ 的行为也很奇特，但与你的问题没有直接关系，因为 __ new __ 是如此奇特它实际上并不一定需要构造任何东西的构造函数 - 完全可以很好地返回现有实例，甚至是非实例......显然Python为你提供了一个很多更多的机制控制。你想到的其他语言，还包括 __ new __ 本身没有自动委托！ - 。

Basically, super-class delegation of the initializer is not automatic in Python for exactly the same reasons such delegation is also not automatic for any other methods -- and note that those "other languages" don't do automatic super-class delegation for any other method either... just for the constructor (and if applicable, destructor), which, as I mentioned, is not what Python's __init__ is. (Behavior of __new__ is also quite peculiar, though really not directly related to your question, since __new__ is such a peculiar constructor that it doesn't actually necessarily need to construct anything -- could perfectly well return an existing instance, or even a non-instance... clearly Python offers you a lot more control of the mechanics than the "other languages" you have in mind, which also includes having no automatic delegation in __new__ itself!-).

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